Projection televisions are well known. In general, a projection television set or projector includes three cathode ray tubes (CRTs), corresponding to the primary colors, red, blue, and green. Associated with each of the CRTs is a projection lens assembly, which is comprised of a plurality of optical lens units. Overall, a CRT has an attached faceplate, and the function of the lens assembly is to magnify the image appearing on the faceplate of the CRT, and thereby project it onto a viewing screen, which is much larger than the faceplate of the CRT. For a typical layout of the optical lens units in a projection television lens assembly see U.S. Pat. No. 4,776,681.
An illustrative, prior art lens cell 10 used in a projection television lens assembly is shown in FIG. 1. Basically, it comprises a plastic tubular member, generally referred to as a lens cell 10. As shown therein, the lens cell 10 itself is further comprised of two corresponding cell halves 12 and 14. The lens cell 10 has grooves which hold the optics or the optical lens units. After the optics are mounted within one of the corresponding cell halves, the other of the cell halves is used to lock in the optics. In the past, cantilever snaps, referred to by reference numeral 13, have been employed to fasten the two cell halves 12 and 14 together, thus ensuring the retention of the optical lens units within the lens cell 10. The most commonly used cantilever snap design has an undercut molded onto the "male" flexing member for engagement with the "female" component, shown in FIGS. 1 and 1A. The cell halves 12 and 14 of the lens cell 10 are assembled together by the use of an assembly fixture that exerts an external force on the cell halves 12 and 14 to engage the cantilever snaps 13. Upon engagement of the cantilever snaps 13, the external force is released and the optics within the lens cell 10 react by pushing back on each of the cell halves 12 and 14. The problem with such a cantilever snap design is that once the optics are mounted within the lens cell 10, the cantilever snaps 13 are usually constantly under load due to the force F.sub.e exerted by the optics. As such, the cantilever snap design fails to provide a retention force that opposes the internal force F.sub.e exerted by the optics, which pushes outwardly against each of the lens cell halves 12 and 14, tending to separate the cell halves 12 and 14. Thus, the constant load causes the cantilever snaps 13 to disengage, resulting in a separation of the cell halves 12 and 14 of the lens cell 10.
An object of the invention is to provide a locking device that ensures retention of the optical lens units within the lens cell. Another object of the invention is to provide a locking device that provides a retention force that opposes the force exerted outward against each of the lens cell halves by the optics within the lens cell. Yet, a further object of the invention is to provide a locking device that can be easily unlocked or disengaged.